The goal of the proposed research is to investigate the sources of rCBF effects obtained in studies of syntactic processing. Previous studies in this laboratory and elsewhere have documented different patterns of rCBF in different groups of subjects on protocols testing syntactic processing in sentence comprehension. The research proposed here will determine whether these different patterns of rCBF reflect different non-linguistic processes that are employed to different degrees by different groups of subjects, or whether they reflect true differences in the localization of particular syntactic operations. The hypotheses that will be tested are: 1. Previously identified variation in rCBF changes associated with syntactic processing in sentence comprehension will be replicated. 2. These changes are due to differences in the use of visual mental images and short-term memory in performing the sentence comprehension task in different groups of subjects. [unreadable] [unreadable]